We used multiple lines from different species that we observed to probe the physical conditions in W28\(\,\) F region. We used RADEXhttp://www.sron.rug.nl/~vdtak/radex/index.shtml [1]} to model the observed line integrated intensity, which is a statistical equilibrium radiative transfer code made available for public use.
It is a useful tool that provides constraints on physical conditions, namely density and kinetic temperature. RADEX computes the excitation of the molecular lines under non-LTE conditions, provided their collisional rate coefficients are available. It estimates line intensities using the escape probability formulation. In order to calculate the escape probabilities, we use the Large Velocity Gradient (LVG) approximation ([2]}, [3]}). Under this approximation the emitted line photons can escape as long as the velocity shift resulting from the velocity gradient is larger than the local line thermal width, which is valid in C-type shocks (see e.g., [4]}). Other assumptions used in RADEX modeling include the source being an isothermal and homogeneous sphere filling the beam of the telescope. A detailed description of our RADEX analysis is described in the Appendix .
